As will be appreciated by those skilled the art, many hand held power tools may pose considerable danger to the operator if not handled with care. Further, even when great care is exercised many of these hand held tools, whether driven by gasoline or electric motors, still inflict many injuries every year to the operators for various reasons. Sometimes the reason is nothing more than momentary carelessness by the operator, but often times the injury occurs because of some malfunction in the operation. For example with respect to hand held saws such as circular saws and even chain saws, striking a hard foreign member with the blade such as, for example, a nail or a hard knot in the wood, has been known to make the saw either kick back or to bind. Since the operator is aware of the danger posed by the saw if not kept under control, in such an emergency the operator's natural tendancy is to grip the handle of the tool or saw more firmly to assure that the saw does not become uncontrolled. Unfortunately, with most such tools the control mechanism such as an on and off switch for an electric motor or the speed control switch of a gasoline motor is usually controlled by one or more fingers of the supporting hand. Thus, when the emergency occurs and the operator grasps the handle more firmly, in the usual case he also inadvertently continues his grasp on the on and off switch or the speed control switch thereby preventing the machine from coming to a halt. It is clear that the operator needs to hold firmly to the tool, while at the same time releasing any pressure on the control member or switch itself. Unfortunately, in a panic situation holding tight on the handle while at the same time releasing the control member usually will just not occur by even the experienced operator.
Therefore, it is an object of the present invention to provide a control member which will deenergize the machine while the operator continues to firmly grip the handle of the machine.
Although an investigation of the prior art indicates that many types of switches for different purposes such as snap action switches used to avoid arcing, switches which incorporate a breaker mechanism for disengaging the electrical power to the switch in the case of an overload, and switches that require a first conscious positive action before the energizing switch can be activated are already available in the prior art. Furthermore, patents disclosing motor driven hand tools using trigger and handle activated motors are also disclosed in the prior art. For example, U.S. Pat. No. 3,292,673 issued to E. J. Gregory on Dec. 20, 1966, discloses a typical circular saw activated by a standard finger switch within the handle illustrative of the common type trigger switch. It is this type of trigger switch that must be released in the case of binding of the saw blade. Yet, since the trigger switch is in the handle the natural tendency of the operator is to squeeze more firmly. The other patents with respect to on and off switches of power tools include U.S. Pat. No. 3,869,590 issued to H. W. Hults on March 4, 1975, U.S. Pat. No. 3,881,081 issued to R. Schilling, et.al. on April 20, 1975, and U.S. Pat. No. 4,286,125 issued to A. Schaffler, et.al. on Aug. 25, 1981. These patents are particularly relevant to providing good on and off contact action, More specifically, these patents disclose snap action electrical switching to avoid arcing within the switch. Also shown are safety guarded switches such that the switch cannot be activated unless clearly intended by the operator. However, none of these patents show any type of secondary switching action such that the switch will go to an off position in an emergency or panic situation.
U.S. Pat. No. 3,009,999 issued to D. W. Johnson on Nov. 21, 1961 and U.S. Pat. No. 4,149,053 issued to Eric L. Long on April 10, 1979 teach safety type switches. For example, the Johnson patent shows a technique whereby the switch also includes an overload sensing capability such that if the saw or machine is used in an electrical overload condition for a predetermined amount of time, the switch will open by means of bimetal elements thereby preventing any damage to the motor of the machine and also preventing further use of the machine until the overload condition is corrected. The Long patent, on the other hand, utilizes a technique, such that in the event the electrical contacts are welded in the closed position by arcing, power may still be removed from a power tool by means of a secondary switching connection which will come into play only when the contacts are in such a welded condition. Thus, according to this patent the tool will be deenergized when the trigger is released even if the contacts are welded closed. However, it can be seen from these patents that neither of them are concerned with the emergency situation where the operator of the circular saw or other machine should be turning the switch off by releasing pressure thereon, but instead in a panic state grips the handle lighter and consequently the switch is gripped even tighter thus maintaining electrical power to the saw.
Therefore, it is another object of this invention to provide switching methods and apparatus wherein panic gripping of the support handle with a switch incorporated therewith results in the machine being deenergized to provide a safe condition.
It is still another object of this invention to provide switching methods and apparatus which incorporate an off-on-off switching arrangement.
It is yet another object of the invention to provide switching methods and apparatus which allow safe deenergization of the machine driven apparatus which are both inexpensive and easy to incorporate.